This invention relates to copolymers of carbon monoxide and .alpha.-olefins, to a catalyst composition for making such copolymers, to a process for making the copolymers, and to articles made from such copolymers.
Linear alternating polymers of carbon monoxide and one or more ethenically unsaturated hydrocarbons are well known. They are generally prepared by contacting the monomers together at an elevated temperature and pressure, in the presence of a solution of catalyst and in a diluent in which the polymers are insoluble or virtually insoluble. The catalyst will typically comprise a palladium compound, an anion of an acid with a pKa of less than 6 (determined in aqueous solution at 18.degree. C), and a bisphosphine of the general formula R.sup.1 R.sup.2 P-R-PR.sup.3 R.sup.4 wherein R.sup.l, R.sup.2, R.sup.3, and R.sup.4 represent aryl groups which may be substituted with polar groups, and R represents a bivalent organic bridging group containing at least two carbon atoms in the bridge.
The anion occurring in the catalyst composition may be in the form of an acid or a salt. Suitable salts include main group metal salts such as tin, aluminum and antimony salts, as well as non-noble transition metal salts, such as copper, nickel and iron salts. Suitable acids, the ultimate selection of which will depend upon the bisphosphine selected, include strong acids with pKa of less than 2, such as perchloric acid, trifluoroacetic acid and para-toluenesulphonic acid, moderately strong acids having a pKa in a range from about 2 to about 4, such as phosphonic acid, tartaric acid and 2,5-dihydroxybenzoic acid, and weaker acids with a pKa in a range from about 4 to about 6, such as acetic acid.
Suitable bisphosphines include those in which aryl groups R.sup.l, R.sup.2, R.sup.3, and R.sup.4 contain no polar substitutes and those in which at least one of the aryl groups contains at least one polar substituent.
Suitable diluents in which the polymerization may be carried out include mono-alcohols, such as methanol, ethanol and propanol, aromatic hydrocarbons, such as toluene, aliphatic esters, such as ethyl acetate and methyl propionate, ketones, such as acetone and methy ethyl ketone, ethers, such as anisole, glycoles, such as ethylene glycol and glycol ethers, such as dimethyl ether of diethylene glycol. Both single diluents and compound diluents such as alcohol/ketone mixtures are suitable.
In the preparation of polymers of carbon monoxide and an .alpha.-olefin using the above catalyst, both reaction rates and the molecular weights of the polymers formed are important. It is desireable to maximize the polymerization rate and also to maximize the molecular weight of the polymer. Although both reaction rates and molecular weights are functions of temperature, reaction rate varies directly with reaction temperature, whereas, molecular weight varies inversely with reaction temperature. In the copolymerization of carbon monoxide with an olefin, the general practice is to conduct the polymerization at such a temperature as to achieve two minimum criteria: a reaction rate of at least 0.1 kg copolymer/gram palladium-hour, and an average molecular weight of the polymers obtained of at least 5000.
These minimum crIteria can generally be achieved when copolymerizing carbon monoxide and ethylene, a C.sub.2 .alpha.-olefin. These carbon monoxide/ethylene copolymers will have very high melting points and should be worked up in a molten condition, usually at a temperature at least 25 C. above the melting point. However, at such high temperatures the polymers have been found to be rather unstable and to exhibit discoloring and disintegration. The incorporation of a third monomer selected from among .alpha.-olefins having from about 3 to about 10 carbon atoms produces a terpolymer having a lower melting point than the carbon monoxide/ethylene copolymer, such that these terpolymers may be worked up at temperatures low enough so that the terpolymer will not exhibit discoloring or disintegration. Of course the higher the C.sub.3 -C.sub.10 .alpha.-olefin content contained in the terpolymer, the lower the terpolymer melting point. These terpolymers have been produced with the above described catalyst under conditions that will meet the minimum criteria above.
When producing copolymers of a carbon monoxide and at least one C.sub.3 -C.sub.10 .alpha.-olefin, using the known processes and catalysts, it has been found that, barring a few exceptions, it is impossible to prepare such copolymers, while at the same time upholding the two minimum criteria of reaction rate and molecular weight.
It is therefore an object of the present invention to provide for an alternating copolymer of carbon monoxide and at least one C.sub.3 -C.sub.10 .alpha.-olefin. It is another object of the present invention to provide articles prepared from such copolymers. It is yet another object of the present invention to provide a process for making the such copolymers.